extending onStart and onEnd events to set a value in the controller

[jcamorgan]

Hi!

This is more of an enhancement request that an issue and I have noticed that is has been brought up previously. Please have a look at my posting on StaceOverflow:

http://stackoverflow.com/questions/19587147/pass-mousedown-and-mouseup-events-from-directive-to-controller-in-angular-slider